The instant invention relates to optical receivers, and more particularly to an optical signal receiver system that provides for 5 signals, namely VCC, Ground, RPM (Receiver input Power Monitor), Data, and Data Bar outputs, using only the four external pins of a conventional TO can package.
Historically, the optical receiver is packaged in a metal housing which usually incorporates the optics as well. One such package is the TO can which, as illustrated in FIG. 1, has four external electrical leads. One of the leads is welded to the case (Pin1—ground) while the other three go inside the case in order to bring out or feed in three additional signals (Pins 2–4).
The schematic of a typical optical receiver is shown in FIG. 2. There are two major components in the receiver, namely the photodiode and the TIA (Transimpedance Amplifier). The ideal hookup for the TIA requires all four pins. These pins are Vcc (voltage supply), Ground, Data and Data Bar outputs. This poses no problem for a standard part configuration.
However, on some designs, there is a need for bringing out another signal from the photodiode called RPM. If this is done, the Data Bar is usually not brought out of the package and the only output signal is Data (FIG. 3). Since Data and Data Bar are compliments of each other, an arrangement that does not have both signals reduces the output signal by half.